In recent years, a wireless communication function has been mounted on not only information processing devices, such as personal computers, and communication terminal devices, such as cellular phones and PDAs (Personal Digital Assistances), but also various types of consumer electronic devices, such as audio devices, video devices, camera devices, printers, and entertainment robots. In addition, the wireless communication function has been mounted on wireless LAN (Local Area Network) access points and small accessory cards. The accessory cards are wireless card modules having both a storage function and a wireless communication function. Known as wireless card modules are for example PCMCIA (Personal Computer Memory Card International Association) type cards, compact flash cards (registered trademark), mini PCI (Peripheral Component Interconnection) cards.
As the wireless communication function has been mounted on various devices, antennas that receive and transmit radio waves have needed various shapes and characteristics. For example, antennas that can select radiations of polarized waves have been needed.
In a real operational environment of a wireless apparatus, because of for example reflection of radio waves by buildings and substances, the radio waves are propagated with various planes of polarized waves. To solve such a problem, so-called polarization diversity that transmits and receives a radio wave by changing the polarization of the antenna for optimal data transmission rate and throughput has been proposed (for example, Japanese Patent Laid-Open Publication No. 2002-92576).
FIG. 13 is a plan view showing a polarization diversity wireless apparatus using two dipole antennas. Disposed on substrates 101a and 101b are dipole antennas 102a and 102b, respectively. The substrates 101a and 101b are disposed in the apparatus so that the dipole antennas 102a and 102b are orthogonally arranged. The dipole antenna 102a is connected to a terminal 104c of a switch 104 through a balance-unbalance converter (balun) 103a. The dipole antenna 102b is connected to a terminal 104b of the switch 104 through a balance-unbalance converter (balun) 103b. A radio frequency is supplied to a terminal 104a of the switch 104.
FIG. 14 is a plan view showing a polarization diversity wireless apparatus using two Zepp antennas. Disposed on substrates 111a and 111b are Zepp antennas 112a and 112b, respectively. The substrates 111a and 111b are disposed in the apparatus so that the Zepp antennas 112a and 112b are orthogonally arranged. The Zepp antenna 112a is connected to a terminal 113c of a switch 113. The dipole antenna 112b is connected to a terminal 113b of the switch 113. A radio wave is supplied to a terminal 113a of the switch 113.
FIG. 15 is a plan view showing a polarization diversity wireless apparatus using two monopole antennas. Disposed on substrates 121a and 121b are monopole antennas 122a and 122b and base plates 123a and 123b, respectively. The substrates 121a and 121b are disposed in the apparatus so that the monopole antennas 122a and 122b are orthogonally arranged. The monopole antenna 122a is connected to a terminal 124c of a switch 124. The monopole antenna 122b is connected to a terminal 124b of the switch 124. The base plates 123a and 123b are grounded. A radio frequency wave is supplied to a terminal 124a of the switch 124.
In the polarization diversity wireless apparatuses shown in FIG. 13 to FIG. 15, when the reception level of one antenna becomes low, the other antenna is selected using the switches 104, 113, and 124 to prevent the quality of the received signal from deteriorating.
As described above, to ideally deal with propagation of a plurality of polarized waves, a plurality of antennas corresponding to various directions of polarized waves are disposed in one apparatus. In this method, however, it is necessary to orthogonally arrange the plurality of antennas. Thus, the area that the antennas occupy becomes large. As a result, the size of the apparatus becomes large. If the antennas are closely disposed in a small occupied area, the antennas interfere with each other. As a result, the radiation patterns of the antennas get distorted.
To solve the foregoing problem, it is thought that a circularly polarized wave micro-strip antenna is used instead of linearly polarized wave antennas that are orthogonally arranged. In this method, with one antenna, polarized waves can be selectively radiated. However, generally, the frequency band of a micro-strip antenna is narrow. For example, the bandwidth of a dipole antenna is around ten percent, whereas the bandwidth of a micro-strip antenna is several percent or less. Although the frequency band of a micro-strip antenna may be widened with parasitic elements, they cause the size of the apparatus to increase.
As described above, conventionally, it is difficult to decrease the area of a plurality of antennas of a polarization diversity wireless apparatus and suppress deterioration of characteristics of the antennas due to interference therebetween. Because of these difficulties, the polarization diversity wireless apparatus is inconsistent with the current engineering tendency of which a wireless apparatus is miniaturized and a wireless communication function is mounted on various consumer devices.
Therefore, an object of the present invention is to provide an antenna apparatus having a plurality of antennas that transmit and/or receive orthogonally polarized waves, and that are closely disposed, and that suppress deterioration of characteristics due to interference therebetween and to provide a wireless apparatus and an electronic apparatus that have the antenna apparatus.